[cfe-dev] Question on VisitVAArgExpr()

[Sylvere Teissier]

Hi,
If we look at the 3 different implementations of VisitVAArgExpr function
in clang source...:

--------------------------------------------------------------------
Value *ScalarExprEmitter::VisitVAArgExpr(VAArgExpr *VE) {
  llvm::Value *ArgValue = CGF.EmitVAListRef(VE->getSubExpr());
  llvm::Value *ArgPtr = CGF.EmitVAArg(ArgValue, VE->getType());

  // If EmitVAArg fails, we fall back to the LLVM instruction.
  if (!ArgPtr)
    return Builder.CreateVAArg(ArgValue, ConvertType(VE->getType()));

  // FIXME Volatility.
  return Builder.CreateLoad(ArgPtr);
}
----------------------------------------------------------------------
ComplexPairTy ComplexExprEmitter::VisitVAArgExpr(VAArgExpr *E) {
  llvm::Value *ArgValue = CGF.EmitVAListRef(E->getSubExpr());
  llvm::Value *ArgPtr = CGF.EmitVAArg(ArgValue, E->getType());

  if (!ArgPtr) {
    CGF.ErrorUnsupported(E, "complex va_arg expression");
    const llvm::Type *EltTy =
      CGF.ConvertType(E->getType()->getAs<ComplexType>()->getElementType());
    llvm::Value *U = llvm::UndefValue::get(EltTy);
    return ComplexPairTy(U, U);
  }

  // FIXME Volatility.
  return EmitLoadOfComplex(ArgPtr, false);
}
-----------------------------------------------------------------------
void AggExprEmitter::VisitVAArgExpr(VAArgExpr *VE) {
  llvm::Value *ArgValue = CGF.EmitVAListRef(VE->getSubExpr());
  llvm::Value *ArgPtr = CGF.EmitVAArg(ArgValue, VE->getType());

  if (!ArgPtr) {
    CGF.ErrorUnsupported(VE, "aggregate va_arg expression");
    return;
  }

  EmitFinalDestCopy(VE, LValue::MakeAddr(ArgPtr, Qualifiers()));
}
-----------------------------------------------------------------------

...there is no fall back to the LLVM va_arg instruction if (ArgPtr==0)
for the aggregate and complex case
Then there is an unsupported error for architectures that don't
implement EmitVAArg...

Why? Is it a bug or is it impossible to use LLVM va_arg instruction for
these cases ?